The present invention relates to a data processing system and, particularly to a data processing system wherein when a host machine makes access to an I/O unit of a local machine, the local machine replaces that input/output operation with the input/output operation of another I/O unit.
In recent years, it is a common practice to organize a computer network system in which a plurality of computer systems are linked with each other. For example, there is known a laboratory automation (LA) control system in which host machines (large computers) and local machines (small computers) are linked together hierarchically. The purposes for organizing a computer system network are to carry out: (1) effective utilization of communication resources, (2) distribution of functions of the communication system, (3) flexible expansion of the communication network, and (4) labor saving in the application system.
As a method of accessing another machine through the communication line, there is known the Virtual Telecommunication Access Method (VTAM), that provides as advantages: (1) a plurality of application programs can be used at one terminal, (2) a plurality of terminals can share one communication line, (3) the application program within a host machine can be used at any location in the network, and (4) the application program need not be aware of the network organization. The computer system network organization and VTAM are described in IBM Systems Journal, Vol. 15, No. 1, 1976; in an article entitled "Synchronous data link control: A perspective", IBM Systems Journal, Vol. 13, No. 2, 1974; and in "VOS3 ECS/VTAM Guide", (manual of Hitachi, Ltd.) 8080-3-140, 1980.
Referring to FIG. 1 showing an example of the inventive system network organization, the prior art system network will first be explained. In FIG. 1, host machines 1 and 2 are linked with each other via communication control computers 3 and 4, respectively, through the communication line. The communication control computers 3 and 4 can be connected in parallel with other machines within the network. A local machine (subsidiary host machine) 5 is linked via a control unit 6 with the communication control computer 3 of the host machine 1 or with other local machines so that they communicate with each other. The control unit 6 controls the communication procedure such as the High-level Data Link Control (HDLC) procedure and Synchronous Data Link Control (SDLC) procedure.
In the conventional system network organization, the application program of the host machine 1 can be used by a data terminal, i.e. I/O unit, 8 of the host machine 2, as well as by a data terminal 7 of the host machine 1. Assuming the application program to be a time sharing system (TSS), the host machine 1 runs a plurality of user programs (TSS-AP) 9 under TSS control program 10, which transacts data with its data terminal 7 and the data terminal 8 of the host machine 2 by using VTAM program 11.
Namely, when a user program 9 outputs a message to the data terminal 7 or 8, it is sent to the terminal 7 or via the communication control computer 4 to the terminal 8 after the HDLC procedure has been processed by Network Control Program (NCP) 13 within the communication control computer 3 following VTAM 11 and operating system (Host OS) 12. Conversely, it is possible for the terminals 7 and 8 to enter messages into the host machine 1 by the reverse process for the above procedure.
It is also possible for terminals 14, 15 and 16 connected to the local machine 5 to use the application program of the host machine 1 or 2. Such local machine 5 is called a local machine with cluster control function.
In the local machine 5, program HICOP (Hitachi Network Architecture Subhost Communication Program) 18 is run under operating system 17, and further, program DSC (Data Stream Compatibility) 19 is run. The HICOP 18 is a program for performing functions equivalent to those of VTAM of the host machine, and the DSC 19 is a program which performs so that the application program 9 in the host machine 1 can access the data terminal units 14, 15 and 16 connected to the local machine 5 in the same way as for the terminal 7.
Thus, owing to VTAM and the cluster control function of the local machine 5, the conventional computer system network has been advantageous in (1) using terminals connected to a local machine as terminals of the host machine, and (2) using the capability and resources of the host machine by the terminals of local machines.
Reference numeral 20 denotes an experimental room of Laboratory Automation System (LA) connected hierarchically with the host machine 1 and local machine 5. The room is equiped with a local terminal 16 and measuring instrument standard interface bus 21, so that control data and measurement data of instruments and experimental apparatus 22 are collected by the local machine 5 and the collected measurement data is stored in a local file 23 which is a file storage of the local machine 5.
Subsequently, the host machine 1 is required for more high-grade analysis for the collected measurement data, and on this account the measurement data stored in the local file 23 is transferred to a host file 24 which is a file storage of the host machine 1, and then the host machine 1 reads out the measurement data from the host file 24 and executes analysis program 9 within the host machine 1. Following the analysis, resultant data in the host file 24 must be transferred back to the local file 23 of the local machine 5. For file transfer, it is a common practice to perform a Remote Job Entry (RJE) function in which a batch job request is issued by the local machine 5 to the host machine 1.
Although this method of requesting the host machine 1 for a job by use, of the RJE function takes little time in transferring data between the local file 23 and the host file 24, such file transfer is carried out as a batch job by the host machine 1, causing a considerable time loss to an extent of 5-10 minutes for a small scale job during the wait time for job execution (or the wait time of job scheduling). Namely, although the conventional system network organization allows the terminal 16 of the local machine 5 to use the application programs 9 for the analysis under the TSS control program 10, in actual practice, it takes a considerable time before the analysis program 9 is operable, resulting in an inefficient use of the hierarchical linkage between the host machine 1 and the local machine 5.